Rechargeable electrochemical cells are enjoying increasing use. Typical of these cells is the sealed spiral wound lead acid cell. This cell can provide long term operation, is substantially maintenance free and offers a high capacity per unit volume. It is also light in weight and rugged in construction, making it especially suited for portable operations.
In view of its beneficial characteristics, the electrochemical cells being described are frequently used in portable arrangements termed "cell packs". Cell packs are groups of electrochemical cells electrically interconnected, in series, parallel, etc., to provide sources of electrical power of varying voltage and rating. Cell packs are now also provided with recharging capability in view of the rechargeability of the component cells. All of these features making cell packs useful for powering a variety of consumer and industrial devices, such as portable televisions, portable flashlights, electric saws and the like.
As the use of rechargeable cell packs expands, so does the need for providing cell packs of greater durability.
Among the problems that can be encountered is the interruption of the cell pack inner circuitry due to sudden impact or exposure to undue vibration. Frequently, because of the portable nature of the packs, they are jolted or jarred during normal use. These collisions can cause undue movement or shifting of the interior cells and can entirely disrupt or short the circuitry, causing the pack to become inoperative and possibly limiting its further use. Frequently also, the constant vibration can cause the inner cell connections to fatigue and eventually break, again limiting the usefulness of the pack.
Repairing broken cell connections can be quite difficult. The packs are generally considered maintenance free and as a result, they usually are not adapted to easy repair. Moreover, among the advantages of these packs is that they can be stored in "out of the way" places in electrical apparatus, permitting the apparatus to be more compact, etc. This however makes access to the cell pack for repair even more difficult and again detracts from the usefulness of the pack.
In view of these difficulties, disrupted or broken interior cell pack connections can motivate the user to replace the entire pack rather than face the difficulty of repair.
One technique for increasing the impact and vibration resistance of electrochemical cell packs is to cement or glue the cells to the casing in an attempt to prevent cell movement or shifting. This alternative, however, can require complex manufacturing procedures and the need for additional materials. Cementing might even require serious modification or even a reconstruction of the individual cells, making the operation even more complex.
Encasing the cells in a vibration resistant material might also be considered. Here again however additional materials would be needed and the additional packing might detract from the desirable compactness of the overall pack.
The foregoing conditions highlight the need for providing a rechargeable electrochemical cell pack which is impact and vibration resistant, compact in size, and which can be fabricated without undue difficulty. It would be further desirable to provide a method for fabricating such an impact resistant electrochemical cell pack from readily available electrochemical cells, without the need for serious modification of the cells or the need for fabrication of new cell structures.
Accordingly, it is an object of the present invention to provide a rechargeable electrochemical cell pack which is impact and vibration resistant, compact in size, and capable of being fabricated in an efficient, economical and convenient manner.
Another object of the invention is to provide a method of making vibration resistant cell packs using commonly available sealed electrochemical cells, without the need for substantial modification of the cells, or the use of complex assembly operations or undue additional materials.
These and other objects of the invention will become apparent from the following summary and description of the invention taken in conjunction with the accompanying drawings.